GB605776A - Improvements in or relating to apparatus for the heat-treatment of metal strip or other elongated metal member - Google Patents

Abstract

605,776. Automatic control systems. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. Sept. 23, 1943, No. 15630. Convention date, Oct 31, 1942. [Class 38 (iv)] [Also in Groups II and XXXVI] An apparatus for heat-treating metal strip or other elongated strip member, comprises a variable speed electric motor means for moving the strip at a variable pre-determined speed in the direction of its length in a gaseous medium, e.g. air; inductive heating means adjacent one section of the path of the strip to cause a current to flow downwardly in the strip and cooling means adjoining the heating means, the relation between the rates of power-input on the speed of the strip being controlled, so as to maintain a substantially predetermined thermal condition of the strip, said control means being directly or indirectly responsive to the thermal condition of the strip. The control means is placed at a pre-determined point near the end of the region where it is heated and may comprise a thermostat, an automatic electrical regulator or a reflected light photo-sensitive device, the latter being used when the strip comprises a relatively high melting point coated with a thin layer of a low-melting point metal such as tin-coated steel strip. As applied to electrolytically tinned steel strip, the loop 1 of steel strip 2 is fed through drag rollers 3 then through the electrolytic lining ball 4, past hot air blowers 5 and then over a roller 6 and downwardly through an induction heating coil 7. Immediately it leaves the coil 7 it is cooled by air from blowers 8, passes down into a quenching tank 9, preferably filled with hot water at 80‹ C. and then round a roller 10 and out through a cranner 11 and rollers 12. The coil 7 is heated by a high-powered oscillation-generator 21 such as is described in Specification 568,463, [Group XL], wh ich is supplied with power from three-phase line 41 through a circuit-breaker 42, regulator 43 to the primary 44 of a step-up rectifier-transformer 45 having two secondary windings 46, 47, the star points of which are joined by transformer 48 whose mid-point is connected to the negative lead 40 constituting the negative bus of the generator 21. The phase-terminal of the secondary windings 46, 47 are connected through rectifiers 49 to the conductor 32 constituting the positive bus. The regulator 43 is adjusted by means of a motor 50 having windings 51, 52 for bucking or boosting the voltage by a conductor 57 from a bus 53 and being controlled by a relay 54 having make-and-break contacts 55, 56. The regulator 43 is controlled by the temperature of the strip 2 near the point where it leaves the coil 7 by a light sensitive means comprising a source of light 67 which sends a beam of light 63 through a window 60 in the coil 7, part of the beam being.reflected from the matte surface of the strip to a photo-electric cell 64 which is in circuit with a supply line 66 from the supply bus 53 and a control-conductor 67, which energizes the relay 54 which then energizes the motor 50 in the voltage-boosting direction, thus increasing the magnitude of the inducing currents, so making the tin coating flow on the surface and the flow line move up higher than the point of infringement of the light beam. The light beam now falls on a shiny surface and is no longer reflected along the line 65, thus de-energizing the photoelectric cell 64 causing the relay 54 to drop down again. An alternative regulating means comprises a watt meter 70 which is energized by transformers 71, 72 from the transformer 45 and is provided with make-and-break contacts 73, 73<SP>1</SP>, the contact arm of which is restrained by a solenoid 74 energized through a conductor 75 from a generator 76 coupled to a motor 15 which, with a motor 14, drives the rollers 3. The coil 7 is divided into coil portions 81, 82, 83; 84 connected in parallel and the frequency of the generator for use with tinned strip is 50-500 kilocycles per second and for wires 20-500 kilocycles per second the energy output being sufficient to heat more than 200 lbs. of the strip more than 300‹ F. per minute. Specification 571,887, [Group XI], also is referred to.